This invention relates generally to refrigeration and air conditioning systems employing multi-stage compressors, and more particularly to a system utilizing a sub-cooler/economizer for sub-cooling the condensed refrigerant prior to vaporization in the evaporator, as well as other unique features and modes of operation, whereby there is provided high flexibility of application while maximizing efficiency.
The invention is particularly suited for supermarket food refrigeration and freezer applications. Current supermarket systems generally comprise three or more single stage fixed capacity compressors of equal or unequal size and all connected in parallel, which are individually turned on and off in response to system load in order to attempt to match same.
The primary objects of the present invention therefore are to provide a refrigeration system which is highly efficient, which has redundancy and reliability, and which has load matching without excessive cycling. More specifically it is the provision of a system which provides relatively constant suction pressure over an extremely wide load range, without signficant loss of efficiency, and which provides for consistent liquid line temperature control, thus facilitating the use of highly efficient liquid-suction heat exchange. A related advantage of the present system is that it permits the discharge pressure to float so that it is unnecessary to provide any artificial head pressure control (i.e., condenser flooding devices, etc.), which unnecessarily load the compressors. The invention also eliminates the need for oil coolers because the refrigerant temperatures are so well controlled. Furthermore, the sub-cooler provides lower pressure drops across the evaporator so that higher suction pressures can be utilized, thereby enhancing efficiency.
Another significant advantage of the refrigeration circuit of the present invention is that it permits the use of R-22 as the sole refrigerant in a given supermarket, both for high and low temperature applications, while providing a performance and efficiency improvement over standard systems.
Another advantage of the present invention is the fact that it provides an inherent improvement in compressor reliability due to lower imposed compression ratios, as compared to standard systems. Furthermore, it provides redundancy of equipment as compared to many existing parallel compressor systems.
Another advantage of the present invention resides in the fact that it utilizes very simple controls to provide highly efficient operation, including accurate suction pressure control as well as reliable liquid line control, as compared with standard systems. Control may be provided by the use of only two basic transducers for total system control.
A further advantage of the present invention resides in the fact that it may be operated in many different highly efficient modes depending on the particular application at hand.